1. Field of the Invention
The present invention relates to electric power distribution systems, and more particularly to a method and apparatus for detecting series and parallel arc faults for electric power systems.
2. Description of the Related Art
Electrical systems used in complex environments such as aerospace systems, industrial environments, vehicles, and residential environments include a large number of electrical circuits, devices, and wires. Arc faults may occur in any of the electrical circuits, or along the wires. If not detected promptly, arc faults may cause short circuits, malfunctions, and fires in the equipment serviced by the electrical circuits or wires exhibiting arc faults.
Arc fault detection and protection pose a significant challenge in such complex environments. Correct and prompt arc fault detection and protection are critical in aircraft environments. Airlines, aircraft manufacturers, the military, and various regulatory agencies have expressed the need for accurate and fast arc fault detection and protection systems, to improve the aircraft wiring safety. A method and system that can reliably detect and prevent series and parallel arcs in electric power systems and enhance wiring system protection, is needed.
Integration of typical/conventional arc fault detection techniques in aircraft electrical systems presents significant challenges. Some of these challenges are associated with the presence of higher and variable AC line frequencies in aircraft systems, a need for DC protection, lack of ground return wires which are typically required for Ground Fault type protection, cross-talk between adjacent wires in the same wire bundle, and a need for zero-tolerance for nuisance trips.
Arc faults in aircraft electric systems can be classified into four categories, based on the methods used to characterize the arcs. Tests used to characterize arcs include the guillotine arc or point contact test, the wet arc or salt water drip test, the loose terminal test, and the carbonized path test. Various arc faults that can be characterized by these tests have different signatures adding challenges to the detection of arc faults. Moreover, some arc fault signatures become inconspicuous in environments that exhibit cross-talk, common source impedance feedback, transient aircraft load characteristics, etc.
Transient aircraft load characteristics pose major challenges for arc detection. Aircraft equipment and standard aircraft loads can produce anomalous waveform signatures during normal operating conditions. Loads and equipment that can produce anomalous waveform signatures include motors (during motor start-up), strobe lights, landing lights, buses (during bus transfers), transformer rectifiers, incandescent and fluorescent lighting loads, and mechanical switches (during opening and closing). Such loads, as well as other transient process conditions can exhibit signatures that mimic, or are indicative of arc conditions. Differentiating such false arc fault alarms from real arc fault occurrences is important on an aircraft.
Some arc fault detection technologies projected for integration in aircraft systems, require understanding and modeling of the arc fault current/voltage signatures and of the normal steady state behavior and transient behavior of the aircraft electric system. Given the large variation in aircraft systems and loads, an algorithm that relies solely on the content of the current/voltage signals cannot be immune to nuisance trips, Hence, such arc fault detection technologies provide unreliable performance.
Disclosed embodiments of this application address these and other issues by utilizing differential arc fault detection methods and apparatuses that detect arc faults using arcing content of current/voltage signals, and eliminate potential nuisance trips by canceling from the sensed current/voltage signals, the content of interferences such as load characteristics, cross-talks, etc. In one embodiment, an arc fault detection master node and slave node sample voltage signals and compare the sampled values to determine whether a series arc has occurred; and sample current signals and compare the sampled values to determine whether a parallel arc has occurred.